1. Field of the Invention
The present invention relates to a method of forming a laminate by laminating an intermediate layer and a metal layer, a method of forming a laminate by laminating a metal layer and a metal oxide layer and a method of manufacturing a photovoltaic device.
2. Related Background Art
As a photovoltaic device having an amorphous semiconductor layer formed of silicon, silicon-germanium or silicon carbide, or a semiconductor layer containing crystal phases including those formed of a microcrystal and a polycrystal of such a material, a device having a reflecting layer formed on the back surface of the semiconductor layer to improve the collection efficiency at long wavelengths has been used. It is desirable that such a reflecting layer exhibit an effective reflection characteristic closer to a band end of the semiconductor material, i.e., in the range of 800 to 1200 nm. Examples of materials sufficiently satisfying this condition are metals such as gold, silver, copper and aluminum, and alloys of these metals.
An arrangement using an optically transparent layer having irregularities to achieve optical confinement has also been used. In general, attempts have been made to enable effective use of reflected light for improvement in short-circuit current density Jsc by forming a laminate in which a metal oxide layer having irregularities is provided between the reflecting layer and the semiconductor layer. Degradation in characteristics due to a shunt path is prevented by providing such a metal oxide layer. Attempts have also been made to increase the optical path length for incident light in the semiconductor layer by providing a metal oxide layer having irregularities on the light incidence side of a semiconductor device for the purpose of enabling effective use of reflected light for improvement in short-circuit current density Jsc.
For example, the achievement of an increase in short-circuit current by an optical confinement effect based on a combination of a reflecting layer formed of silver atoms and having irregularities and a zinc oxide layer is described in P-IA-15 a-SiC/a-Si/a-SiGe Multi-Bandgap Stacked Solar Cells With Bandgap Profiling Sannomiya et al., Technical Digest of the International PVSEC-5, Kyoto, Japan, p387, 1990, and other documents. Japanese Patent Application Laid-Open No. 8-217443 discloses a method of uniformly forming a zinc oxide thin film having an improved transmittance by performing electrolysis in an aqueous solution containing zinc ions and nitric acid ions.
In Japanese Patent Application Laid-Open No. 6-204515 is described the construction of stainless substrate/Ti/Ag/ZnO/Si and is disclosed use of a Ti layer for improving the adhesion to the substrate.
Further improvements in the characteristics of the reflecting layer and the metal oxide layer are being pursued to improve the characteristics of photovoltaic devices. Also there is a problem that a photovoltaic device becomes deteriorated in photoelectric conversion characteristics and durability, for example, due to a reduction in reflectance of a metal layer, a reduction in transmittance of a transparent electroconductive layer or a reduction in adhesion between adjacent layers in a case where the photovoltaic device is used under high-temperature and high-humidity conditions or used through a long period of time, in a case where a plurality of the photovoltaic devices are used in a state of being connected in series, and where the photovoltaic devices are maintained in a state of partially irradiated with light for a long time, or in a case where a voltage with a polarity opposite to that of the voltage generated by normal photoelectric conversion is applied to part of a plurality of photovoltaic devices not irradiated with light.